Abstract
During the exploitation of low permeability gas-condensate reservoirs, the mud filtrate, acidizing liquid, and fracturing fluid invade the reservoir and condensate gas, severely reducing the permeability of the reservoirs due to increased capillary pressure and water wettability. For the current paper, an oligomeric silicone surfactant (OSSF) containing sulfonic acid groups was synthesized to improve the flowback of such fluids. The critical micelle mass concentration and critical surface tension were determined by equilibrium surface tension. The surface tension increased with the hot rolling temperature and decreased with the addition of NaCl, KCl, or CaCl2. When the concentration exceeded critical micelle mass concentration, a micelle was formed and its size increased with mass concentration. OSSF adsorption through solid–liquid surface changed the surface chemical composition of the cores and transferred the wettability of cores from water-wet to preferential gas-wet by decreasing the surface energy. At the same time, the increasing temperature led to a change in the adsorption isotherm of quartz sand from Langmuir type (L-type) to “double plateau” type (LS-type) in the OSSF solution. In addition, NaCl decreased the relative foam volume of OSSF while extending the half-life. OSSF decreased the initial foaming volume and stability of the induction period and accelerated sodium dodecyl benzene sulfonate (SDBS) formation.
Highlights
Many low permeability gas-condensate reservoirs possess small reservoir pores and throats wetted by water, which can generate high capillary pressure
Since gas condensate cannot spread on the pore surface wetted by water, it results in the throat being plugged leading to a sharp decrease in gas relative permeability
Since the inorganic ions can adsorb around the surfactant molecules by surface tension of the oligomeric silicone surfactant (OSSF) solution, where the descending order is 10.00 wt % KCl, 10.00 wt % NaCl, electrostatic interaction, the charge number and concentration of inorganic ions that coexist in solution and 0.50 wt % CaCl2
Summary
Many low permeability gas-condensate reservoirs possess small reservoir pores and throats wetted by water, which can generate high capillary pressure. Hydrocarbon and fluorocarbon surfactants are the most commonly utilized surfactants in oil and gas development Hydrocarbon surfactants, such as Emulsifier OP-10, Sodium dodecyl benzene sulfonate (or ABS in short), and Lauryl benzene sulfonate diethanolamine salt (or ABSN in short), are inexpensive and environmentally friendly, they can reduce the surface tension between gas and liquid to 30–35 mN/m, and they are widely used in emulsions, foaming agents, and capillary pressure reduction. They are unable to alter the wettability of reservoirs from water-wet to preferential gas-wet by adsorption. Our accumulated results provide a theoretical basis for expanding the application of silicone surfactants in low-permeability condensate reservoirs
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